Day and night existed long before the first primitive cells came into being. And that light/dark cycle left its mark on nearly every living thing. Microbes, plants, insects, mammals—we all experience circadian rhythms, due to molecular clocks in our cells. But that internal timer affects more than just bedtime. The body's cells may actually divide by the clock too—in fruit flies, at least.

Researchers gave fruit flies a form of inflammatory bowel disease. In response, the flies' intestinal stem cells got busy repairing the gut, most of them dividing in sync around dawn. But when researchers blocked the action of two clock genes in the intestine, the flies couldn't patch up the damage. Instead of a coordinated repair, the cells stalled in various stages of division, indicating that the internal clock plays a role in healing, too. Those results appear in the journal Cell Reports. [Phillip Karpowicz et al., The Circadian Clock Gates the Intestinal Stem Cell Regenerative State]

The researchers say the circadian clock might inform healing in us too, since it's such an ancient trait. If so, they say doctors might want to time surgeries or chemotherapy for when the body is primed to heal, helping patients clock a faster recovery.

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